Fix DWARF parsing for (some) opaque Swift types.

The only thing that prevented this test from working was the fact that
DWARFASTParserSwift expected an Archetype name in the typedef.

rdar://115997836

Author: adrian-prantl

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserSwift.cpp

@@ -166,7 +166,7 @@ lldb::TypeSP DWARFASTParserSwift::ParseTypeFromDWARF(const SymbolContext &sc,
           m_swift_typesystem.GetTypeFromMangledTypename(mangled_name);
   }
 
-  if (!compiler_type && name) {
+  if (!compiler_type && die.Tag() == DW_TAG_typedef) {
     // Handle Archetypes, which are typedefs to RawPointerType.
     llvm::StringRef typedef_name = GetTypedefName(die);
     if (typedef_name.startswith("$sBp")) {

lldb/test/API/lang/swift/opaque_type/Makefile

@@ -0,0 +1,2 @@
+SWIFT_SOURCES := main.swift
+include Makefile.rules

lldb/test/API/lang/swift/opaque_type/TestSwiftOpaqueType.py

@@ -0,0 +1,17 @@
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbutil as lldbutil
+import unittest2
+
+
+class TestSwiftOpaque(TestBase):
+
+    @swiftTest
+    def test(self):
+        """Test opaque types in parameter positions"""         
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "break here",
+                                          lldb.SBFileSpec("main.swift"))
+        self.expect("v p", substrs=["C", "23"])
+

lldb/test/API/lang/swift/opaque_type/main.swift

@@ -0,0 +1,11 @@
+protocol P {}
+
+class C: P {
+  let i = 23
+}
+
+func f(_ p : some P) {
+  print("break here")
+}
+
+f(C())